Submergible pumps are used in a wide variety of environments. One exemplary environment is a subsurface oil reservoir. A submergible pumping system, having a submergible, centrifugal pump, is inserted into the subsurface oil via a wellbore to permit the pumping of oil to a point at or above the surface. The typical submergible pump includes several impellers mounted to a shaft for rotation within an outer housing of the pump. A diffuser cooperates with each impeller to guide the fluid in the direction of flow from one impeller to the next sequential impeller.
Often, the fluid is pumped vertically upward which creates a downthrust at each impeller. The downthrust must be absorbed by some type of bearing or bearings to avoid damage to the submergible pump. Typically, this downthrust is absorbed at each stage, i.e., at each impeller/diffuser, or by a single large thrust bearing disposed somewhere beneath the entire series of impellers and diffusers. The present invention addresses submergible, centrifugal pumps that attempt to receive and handle the downthrust at each stage, sometimes referred to as floating-pump systems.
The downthrust created by the pumping action is handled at each stage by a stationary support that effectively supports each rotating impeller. For example, each stationary diffuser may include a diffuser pedestal on which the next upwardly sequential impeller is supported. Typically, a thrust washer is disposed between the diffuser pedestal and the supported surface of the impeller. Alternatively, a diffuser thrust pad is mounted to or with each diffuser to, again, provide a support platform on which the next upwardly sequential impeller rests. A thrust washer is disposed between the diffuser thrust pad and the supported surface of the impeller.
With either of the above designs, the diffuser pedestal and the thrust pad generally have complex shapes that are expensive to manufacture. For example, the typical thrust pad is made from an extremely hard material and includes a flared upper region having a top surface over which the thrust washer slides during rotation of the adjacent impeller. Because of the type of material used in the thrust pad, it is relatively expensive to machine flared, curved, or expanded regions. Similarly, it is relatively expensive to form the integral diffuser pedestal.
It would be advantageous to create a relatively simple diffuser bushing having an outer surface with a generally constant radius to simplify the machining and thereby reduce the cost of the overall submergible pump.